Doubt

There is nothing more dreadful than the habit of doubt. Doubt separates people. It is a poison that disintegrates friendships and breaks up pleasant relations. It is a thorn that irritates and hurts, it is a sword that kills. Neither naked asceticism, matted hair, dirt, fasting, sleeping on the ground, dust and mud, nor prolonged sitting on one's heels can purify a man who is not free of doubts.

-Siddartha Gautama